Discuss the position of hydrogen in the modern periodic table.
(N/A) Hydrogen is the first element in the periodic table. Its placement has been a subject of discussion due to its unique properties.
$1$. Resemblance to alkali metals: Hydrogen has an electronic configuration of $1s^1$, which is similar to the outer electronic configuration $(ns^1)$ of alkali metals (Group $1$). Like alkali metals, it forms unipositive ions $(H^+)$ and forms oxides, halides, and sulfides.
$2$. Resemblance to halogens: Like halogens (Group $17$), hydrogen is short by one electron to achieve the nearest noble gas configuration. It forms a diatomic molecule $(H_2)$ and forms covalent compounds.
$3$. Differences: Unlike alkali metals, hydrogen has a very high ionization enthalpy $(1312 \text{ kJ mol}^{-1})$ and does not possess metallic characteristics. Unlike halogens, its reactivity is much lower.
$4$. Unique nature: The loss of an electron from a hydrogen atom results in a nucleus $(H^+)$ of size $\sim 1.5 \times 10^{-3} \text{ pm}$, which is extremely small compared to normal atomic/ionic sizes ($50$ to $200 \text{ pm}$). Consequently, $H^+$ does not exist freely.
Conclusion: Due to these unique properties, hydrogen is best placed separately in the periodic table.
$1$. Resemblance to alkali metals: Hydrogen has an electronic configuration of $1s^1$, which is similar to the outer electronic configuration $(ns^1)$ of alkali metals (Group $1$). Like alkali metals, it forms unipositive ions $(H^+)$ and forms oxides, halides, and sulfides.
$2$. Resemblance to halogens: Like halogens (Group $17$), hydrogen is short by one electron to achieve the nearest noble gas configuration. It forms a diatomic molecule $(H_2)$ and forms covalent compounds.
$3$. Differences: Unlike alkali metals, hydrogen has a very high ionization enthalpy $(1312 \text{ kJ mol}^{-1})$ and does not possess metallic characteristics. Unlike halogens, its reactivity is much lower.
$4$. Unique nature: The loss of an electron from a hydrogen atom results in a nucleus $(H^+)$ of size $\sim 1.5 \times 10^{-3} \text{ pm}$, which is extremely small compared to normal atomic/ionic sizes ($50$ to $200 \text{ pm}$). Consequently, $H^+$ does not exist freely.
Conclusion: Due to these unique properties, hydrogen is best placed separately in the periodic table.
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Similar Questions
State True or False for the following statements:
$1$. Metals of group $7$,$8$ and $9$ form non-stoichiometric hydrides.
$2$. Pure dihydrogen is obtained by heating hydrocarbons with $H_2O$ vapour in the presence of a $Ni$ catalyst at $1270 \ K$.
$3$. The ionization enthalpy of hydrogen is higher than that of alkali metals.
$4$. Some chemical properties of hydrogen resemble both metals and non-metals.
$1$. Metals of group $7$,$8$ and $9$ form non-stoichiometric hydrides.
$2$. Pure dihydrogen is obtained by heating hydrocarbons with $H_2O$ vapour in the presence of a $Ni$ catalyst at $1270 \ K$.
$3$. The ionization enthalpy of hydrogen is higher than that of alkali metals.
$4$. Some chemical properties of hydrogen resemble both metals and non-metals.
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$(i)$ $CaH_2$,$BeH_2$ and $TiH_2$ in order of increasing electrical conductance.
$(ii)$ $LiH$,$NaH$ and $CsH$ in order of increasing ionic character.
$(iii)$ $H-H$,$D-D$ and $F-F$ in order of increasing bond dissociation enthalpy.
$(iv)$ $NaH$,$MgH_2$ and $H_2O$ in order of increasing reducing property.
$(i)$ $CaH_2$,$BeH_2$ and $TiH_2$ in order of increasing electrical conductance.
$(ii)$ $LiH$,$NaH$ and $CsH$ in order of increasing ionic character.
$(iii)$ $H-H$,$D-D$ and $F-F$ in order of increasing bond dissociation enthalpy.
$(iv)$ $NaH$,$MgH_2$ and $H_2O$ in order of increasing reducing property.
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